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#### 3.1.2 Missing Data

It is possible to represent missing data explicitly in Octave using `NA` (short for “Not Available”). Missing data can only be represented when data is represented as floating point numbers. In this case missing data is represented as a special case of the representation of `NaN`.

: val = NA ¶
: val = NA (n) ¶
: val = NA (n, m) ¶
: val = NA (n, m, k, …) ¶
: val = NA (…, "like", var)) ¶
: val = NA (…, class) ¶

  Return a scalar, matrix, or N-dimensional array whose elements are all equal to the special constant used to designate missing values.

  Note that NA always compares not equal to NA (NA != NA). To find NA values, use the `isna` function.

  When called with no arguments, return a scalar with the value ‘`NA`’.

  When called with a single argument, return a square matrix with the dimension specified.

  When called with more than one scalar argument the first two arguments are taken as the number of rows and columns and any further arguments specify additional matrix dimensions.

  If a variable var is specified after `"like"`, the output val will have the same data type, complexity, and sparsity as var.

  The optional argument class specifies the return type and may be either `"double"` or `"single"`.

  See also: isna.

: isna (x) ¶

  Return a logical array which is true where the elements of x are NA (missing) values and false where they are not.

  For example:

      isna ([13, Inf, NA, NaN])
           ⇒ [ 0, 0, 1, 0 ]

  See also: isnan, isinf, isfinite.

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